Allow students to ask a question on an exercise

[pdawyndt]

Also allow students to directly ask a question on an exercise, not a specific submission. Dries Benoit mentioned that this would also allow students to ask questions on reading assignments (where there are no submissions). Will also be handy to give students the opportunity to ask questions during evaluations/exams.

More info: #1788

[pdawyndt]

Extension: ask question on series or course

[BTWS2]

@pdawyndt Asking a question on a reading activity seems the most useful to me. If something isn't clear in a learning path, students currently can't ask a question about it. I put the explanation for an evaluation (test/exam) in a reading activity. It would be great if they can ask question there.

If you have a question about an exercise you can already ask a general question. The question in combination with a submission motivates students to try something.

Asking questions on series or courses would clutter the UI I think and would result in general questions better suited for e-mail.

Edit: can you update the title to also include reading activities?